The present invention relates to an artificial joint. More particularly, the present invention relates to an artificial joint in which cement filled in a bone cavity of a human femur at the time of implantation can be easily effused upward while the cement mantle might have guaranteed minimal thickness everywhere inside the femur along with correct posture of stem. Any direct contact of the stem with the bone inside femoral canal may evoke early failure of the stem due the passage of the wear material to the bone through the hole in the cement mantle once the debonding of the stem with the cement occurred.
In general, an artificial joint includes an acetabulum portion and a femur portion. The femur portion is made of metal or ceramic and the acetabulum portion is made of polyethylene, or both of the femur portion and the acetabulum portion are made of ceramic.
When implanting the cemented artificial hip joint into the human body, the femoral canal should be reamed and cleaned. After filling cement in, a stem of the artificial joint should be inserted in such correct posture that the cement mantle should cover the stem completely with uniform thickness inside the femur.
At that time, the cement for fixing the human femur and the stem of the artificial joint has not a chemical fixation power and the fixation of the human femur and the stem of the artificial joint are accomplished by means of merely physical bonding.
The conventional artificial joint implanted as above described is disclosed in Korean Patent Publication No.85-1814, filed by and permitted to the present applicant, and will be explained with reference to FIG. 1.
The artificial joint is composed of a head 2, a neck 3, a collar 4 and a stem 5 from the upper portion, incorporated together. The edge of the collar 4 is curved to adhere closely to an upper end of a cortical bone of the human femur. An upper cross section of the stem 5 is an ellipse shape close to a circle and toward below, the cross section of the stem 5 becomes more close to a circle. This shape of the stem 5 can prevent a torsion due to a perpendicular pressure applied from the upper of the stem and a horizontal force applied to the stem.
A wing 7 with a suitable thickness is protruded in a longitudinal direction on an upper-outer surface of the stem 5 so that it can prevent the artificial joint from rotating in the human femur due to a torque in any direction. A center of the wing 7 is formed with a fixing hole 8 for fixing the wing 7 to the human femur.
A plurality of steel wire holes 7 with a suitable pitch are formed in the longitudinal direction of the stem 5 in an inner side of the wing 7, and a chain type of steel wires 10 are inserted into the steel wire holes 9 and wind the surface of the stem 5. The whole surface of the stem 5 including a portion wound with the steel wires 10 is coated with cement 6 having a suitable thickness. This coating of the cement can facilitate the bonding of the cement coated on the whole surface of the stem 5 and the cement filled in the human femur and can decrease an amount of cement used in implantation to diminish an amount of heat generated in curing.
When implanting the aforementioned artificial joint into the femur of human body, femoral cavity should be enlarged by reaming so that the stem 5 of the artificial joint 1 can be inserted into the bone cavity of the human femur along with suitable amount of cement being filled in the bone cavity of the human femur. Thus, the stem 5 is inserted into the bone cavity of the human femur filled with the cement. The cement filled in the bone cavity of the human femur is bonded to the cement 6 coated in advance on the surface of the stem 5, thereby fixedly adhering the stem 5 to the human femur.
When implanting the conventional artificial joint into the human body, as the stem 5 is inserted, the cement filled in the femoral cavity of the human femur should be effused along the surface of the stem 5 and adhered to the cement coated in advance of the surface of the stem 5. However, there is no effusion path for effusing the cement filled in the bone cavity of the human femur, so that the effusion of the cement filled in the bone cavity is not easy. The cement filled in the bone cavity of the human femur is adhered to the smooth surface of the cement 6 coated in advance on the surface of the stem 5 and thus, the adhesion power is small.
The conventional artificial joint has not an absorbing means for absorbing stress concentrated in the cement in the activity of the human body, so that a large load is applied to the stem of the artificial joint to shorten a lifetime of the artificial joint.
Therefore, the present invention is made in order to solve the aforementioned problems. An object of the present invention is to provide an artificial joint capable of facilitating the effusion of cement during implantation of the artificial joint and firmly bond the artificial joint with the human femur along with complete encapsulation of stem with cement inside the femoral canal.
Another object of the present invention is to provide an artificial joint capable of reducing stress applied to the cement.
The above objects can be accomplished by an artificial joint including a head, a neck and a stem and being implanted into a bone cavity of a human femur, said stem coated in advance with cement so as to easily bond the cement to cement used at the time of implantation and to diminish quantity of heat generated when cured, wherein a effusion path is formed in a longitudinal direction on a surface of the cement coated on said stem, so that the cement filled in the bone cavity can be easily effused upward through said effusion path when said stem is inserted into the bone cavity. Complete encapsulation of stem with cement inside the femoral canal is also a strong benefit of precoating. Any direct contact of stem with bone will provide a path for the wear particle to the bone causing osteolysis at the site.
It is preferable that a slot for absorbing stress is further formed in an upper portion of said stem.
It is more preferable that said slot has a slope of 20xc2x0 with respect to the surface of said stem.
Preferably, an inner end of said slot has a spherical shape so that cracks due to concentration of the stress should not be generated.
More preferably, said effusion path is made of one or more grooves with a saw-toothed cross section.
It is still more preferable that said effusion path is formed on the entire surface of the cement coated on said stem or on predetermined positions of the surface of the cement coated on said stem.
Also, the above objects are accomplished by an artificial joint including a head, a neck and a stem and being implanted into a bone cavity of a human femur, said stem coated in advance with cement so as to easily bond the cement to cement used at the time of implantation and to diminish quantity of heat generated when cured, wherein a slot for absorbing stress is further formed in an upper portion of said stem.
It is preferable that said slot has a slope of 20xc2x0 with respect to the surface of said stem.
More preferably, an inner end of said slot has a spherical shape so that cracks due to concentration of the stress should not be generated.